The chemical water treatment industry has historically been involved with reducing or inhibiting the inherent scale forming or fouling tendencies of natural waters associated with large industrial cooling water systems. Many of the foulant components found in water systems originate with the incoming supply, but some contaminants enter the system from the local environment or from process contamination.
Fouling is an extremely complex phenomenon. From a fundamental point of view, it may be characterized as a combined momentum, heat and mass transfer problem. In many instances, chemical reaction kinetics is involved, as well as solubility characteristics of salts in water and corrosion technology. It has been stated that if the fouling tendency of a cooling water can be accurately predicted before a plant is designed and built, significant capital savings might be realized through more accurate heat exchanger specifications.
Usually, it is a normal practice to increase heat exchanger surface area to overcome losses in performance caused by fouling deposits with such additional surface area often accounting for more than half of the actual surface are of the heat exchanger. When such design practice is employed with titanium, stainless steel and like expensive materials of construction, it can be appreciated that capital expenditures might be significantly reduced if data could be developed to anticipate and provide for an antifoulant protocol.
Fouling of a heat transfer surface is defined as the deposition on a surface of any material which increases the resistance to heat transfer. The fouling tendency of a fluid in contact with a heat transfer surface is a function of many variables including the components of the fluid, which in the case of water include, inter alia, crystals, silt, corrosion products, biological growths, process contaminates, etc. Generally, deposits are comprised of a combination of several of these materials in relationship to, inter alia, the geometry of the heat transfer surface, materials of construction, temperature, etc. and thus, chemical inhibitors to solve the problem of a particular deposit involves a variety of different chemicals introduced at varying concentration and at varying times.
Industry has been relegated to the use of laboratory simulators or time lapse evaluations of process heat exchangers and test heat exchangers with the requirement that such equipment is taken off line, shut down, opened and inspected to evaluate fouling problems and antifoulant protocols. In the case of process heat exchangers, such inspection usually results in significant plant down time and lost production. Evaluation covers the entire period of process operation and shows accumulated results, which include system upsets, process leaks, the loss of chemical feed or human errors. While the sampling and laboratory testing of fluids permits evaluation of the fluids, the results of laboratory testing are tedious and do not provide results of simultaneous evaluation.